Spoiling the ship for a ha'pence of tar

So the advice I received after yesterday's post was to remove the rotted siding. And of course what I had forgotten is the possible damage to the framing behind the redwood. Because this door was installed so badly we get leaking inside around the bottom. It's possible that we'll open up a whole can of worms by taking off the siding (a section 6' long by 6" wide).
Let this be a warning to all who need windows and doors installed. You can buy the best windows in the world but their ability to keep out the elements will be totally dependent on the installation. Maybe I shouldn't panic yet but I have a feeling this could turn into a very expensive job.
Rats, rats, rats.